Pulse oximetry provides a noninvasive procedure for measuring the oxygen status of circulating blood and has gained rapid acceptance in a wide variety of medical applications, including surgical wards, intensive care and neonatal units, general wards, and home care and physical training. A pulse oximetry system has a physiological sensor applied to a patient, a monitor, and a patient cable connecting the sensor and the monitor. The sensor has light emitters and a detector, which are attached to a tissue site, such as a finger. The patient cable transmits emitter drive signals from the monitor to the sensor. The emitters respond to the drive signals so as to transmit light into the tissue site. The detector is responsive to the emitted light after attenuation by pulsatile blood flowing in the tissue site, generating a detector signal to the monitor. The monitor processes the detector signal to provide a numerical readout of physiological parameters such as oxygen saturation (SpO2) and pulse rate.
FIG. 1 illustrates portions of a pulse oximetry system 100 having a monitor 110, a sensor 120 and a patient cable 130 interconnecting the monitor 110 and sensor 120. The sensor 120 has LEDs 121, 125 capable of emitting light having two wavelengths into a tissue site. The LEDs 121,125 are configured in a back-to-back arrangement so that a first contact 132 is connected to a first LED cathode 122 and a second LED anode 127. A second contact 134 is connected to a first LED anode 123 and a second LED cathode 126. The monitor 110 has a first driver 112 and a second driver 114. The first contact 132 is in communications with a first driver 112 and the second contact 134 is in communications with a second driver 114. The first LED 121 is activated when the first driver 112 is pulled to Vcc and the second driver 114 provides a current sink to ground. The second LED 125 is activated when the second driver 114 is pulled to Vcc and the first driver 112 provides a current sink to ground. Pulse oximeters capable of reading through motion induced noise are available from Masimo Corporation (“Masimo”) of Irvine, Calif. Pulse oximeters capable of reading through motion induced noise are also disclosed in at least U.S. Pat. Nos. 6,770,028, 6,658,276, 6,157,850, 6,002,952 5,769,785, and 5,758,644, which are assigned to Masimo and are incorporated by reference herein.